The Red River mudpuppy ("Necturus maculosus louisianensis"), also called Louisiana waterdog, is a subspecies of mudpuppy. Some herpetologists consider this salamander to be a full species ("Necturus louisianensis).

The dwarf waterdog ("Necturus punctatus") is the smallest member of the family Proteidae, and is endemic to the United States.

The Neuse River waterdog, "Necturus lewisi", is a medium-sized newt, family Proteidae, found in two rivers of North Carolina.

The Gulf Coast waterdog ("Necturus beyeri") is a species of aquatic salamander in the family Proteidae. It is native to the southeastern United States, where it occurs in Alabama, Florida, Georgia, Louisiana, Mississippi, and Texas. This may be a species complex that could be split into different taxa as research indicates. It is closely related to "Necturus alabamensis".

The Alabama waterdog ("Necturus alabamensis") is a medium-sized perennibranch salamander inhabiting rivers and streams of Alabama. It is listed as endangered by the IUCN.

This animal is most notable for its adaptations to a life of complete darkness in its underground habitat. The olm's eyes are undeveloped, leaving it blind, while its other senses, particularly those of smell and hearing, are acutely developed. It also lacks any pigmentation in its skin. It has three toes on its forelimbs, but only two toes on its hind feet. It also exhibits neoteny, retaining larval characteristics like external gills into adulthood, like some American amphibians, the axolotl and the mudpuppies ("Necturus"). The olm is the only species in the genus "Proteus" and the only European species of the family Proteidae, whose other extant genus is "Necturus".

Axolotls should not be confused with waterdogs, the larval stage of the closely related tiger salamanders ("A. tigrinum" and "A. mavortium"), which are widespread in much of North America and occasionally become neotenic. Neither should they be confused with mudpuppies ("Necturus" spp.), fully aquatic salamanders which are not closely related to the axolotl but bear a superficial resemblance.

Unlike some other neotenic salamanders (sirens and "Necturus"), axolotls can be induced to metamorphose by an injection of iodine (used in the production of thyroid hormones) or by shots of thyroxine hormone. The adult form resembles a terrestrial plateau tiger salamander, but has several differences, such as longer toes, which support its status as a separate species.

Even though they eat fish eggs, negative effects on fish populations have not been documented. Fishermen have been known to catch mudpuppies, sometimes in large numbers, but most often when ice fishing. Necturus salamanders also commonly feed on mollusks, worms, insects and small fish.

Proteidae, is divided into two extant genera, "Necturus" with five North American species, and "Proteus" with one extant European species. They represent an ancient group, known from fossils since the Miocene. However, molecular data and a Laurasian distribution suggest origins that go further back.

While the general opinion is that TFM typically does not harm other fish (due to the relationship between true fish and lampreys), lampricide can be problematic for many amphibians, such as mudpuppies (genus "Necturus") which often share the same habitats. Also, some more "primitive" species of fish, such as the sturgeon in the Great Lakes are sensitive to chemicals such as TFM.

The family Proteidae is a group of aquatic salamanders found today in the Balkan Peninsula and North America. The range of the genus "Necturus" runs from southern central Canada, through the midwestern United States, east to North Carolina and south to Georgia and Mississippi. The range of the olm, the only extant member of the genus "Proteus", is limited to the Western Balkans.

Necturus is a genus of aquatic salamanders endemic to the eastern United States and Canada. They are commonly known as waterdogs and mudpuppies. The common mudpuppy "(N. maculosus)" is probably the best-known species – as an amphibian with gill slits, it is often dissected in comparative anatomy classes.

Members of "Necturus", commonly called "mudpuppies," or "waterdogs," prefer shallow lakes and streams that have slow moving water and rocks to hide under, but have been found in up to 90 feet of water. Their name originates from the misconception that they make a dog-like barking sound. Diet consists of small fish and many invertebrates, including crayfish, snails, and worms. Mudpuppies mature at four to six years and can live to be more than twenty years old. Progenesis is common for mudpuppies, enabling them to reach sexual maturity in their larval stage.

Respiration differs among the different species of salamanders, and can involve gills, lungs, skin, and the membranes of mouth and throat. Larval salamanders breathe primarily by means of gills, which are usually external and feathery in appearance. Water is drawn in through the mouth and flows out through the gill slits. Some neotenic species such as the mudpuppy ("Necturus maculosus") retain their gills throughout their lives, but most species lose them at metamorphosis. The embryos of some terrestrial lungless salamanders, such as "Ensatina", that undergo direct development, have large gills that lie close to the egg's surface.

Existence of potassium siphoning was first reported in 1966 study by Orkand et al. In the study, optic nerve of Necturus was dissected to document the long-distance movement of potassium after the nerve stimulation. Following the low frequency stimulation of .5 Hz at the retinal end of the dissected optic nerve, depolarization 1-2mV was measured at astrocytes at the opposite end of the nerve bundle, which was up to several millimeters from the electrode. With higher frequency stimulation, higher plateau of depolarization was observed. Therefore, they hypothesized that the potassium released to extracellular compartment during axonal activity entered and depolarized nearby astrocytes, where it was transported away by unfamiliar mechanism, which caused depolarization on astrocytes distant from site of stimulation. The proposed model was actually inappropriate since at the time neither gap junctions nor syncytium among glial cells were known, and optic nerve of Necturus are unmyelinated, which means that potassium efflux occurred directly into the periaxonal extracellular space, where potassium ions in extracellular space would be directly absorbed into the abundant astrocytes around axons.

The common mudpuppy ("Necturus maculosus") is a species of salamander in the genus "Necturus". They live an entirely aquatic lifestyle in the eastern part of North America in lakes, rivers, and ponds. They go through paedomorphosis and retain their external gills, thus resembling axolotls. Because skin and lung respiration alone is not sufficient for gas exchange, mudpuppies must rely on external gills as their primary means of gas exchange. They are usually a rusty brown color and can grow to an average length of . Mudpuppies are nocturnal creatures, and only come out during the day if the water in which they live is murky. Their diets consist of almost anything they can get in their mouths, including insects, earthworms, mollusks, and annelids. Once a female mudpuppy reaches sexual maturity, at six years of age, she can lay an average of 60 eggs. In the wild, the average lifespan of a mudpuppy is 11 years. Because of their prevalence and larger size than other salamanders, mudpuppies are good organisms for dissections.

In contrast to many salamanders, proteids never lose their gills during maturation from larvae. This aspect of their physiology is known as pedomorphosis. Despite having lungs, which appear to provide little use in respiration, mudpuppies spend their entire lives underwater. The adult gills resemble fish gills in many ways, but differ from fish gills in that they are external and lack any form of operculum or covering. The bright red exposed gills are often found closed against the body in cool, highly oxygenated water. In warmer, poorly oxygenated water, the gills expand to increase water circulation and provide greater surface area for oxygen intake. Necturus salamanders such as "mudpuppies" also absorb oxygen through their skin and by occasionally breathing air at the surface.

The hellbender has a few characteristics that make it distinguishable from other native salamanders, including a gigantic, dorsoventrally flattened body with thick folds travelling down the sides, a single open gill slit on each side, and hind feet with five toes each. Easily distinguished from most other endemic salamander species simply by their size, hellbenders average up to 60 cm or about 2 ft in length; the only species requiring further distinction (due to an overlap in distribution and size range) is the common mudpuppy ("Necturus maculosus"). This demarcation can be made by noting the presence of external gills in the mudpuppy, which are lacking in the hellbender, as well as the presence of four toes on each hind foot of the mudpuppy (in contrast with the hellbender's five). Furthermore, the average size of "C. a. alleganiensis" has been reported to be 45–60 cm (with some reported as reaching up to 74 cm or 30 in), while "N. m. maculosus" has a reported average size of 28–40 cm in length, which means that hellbender adults will still generally be notably larger than even the biggest mudpuppies.

At hatching, a typical salamander larva has eyes without lids, teeth in both upper and lower jaws, three pairs of feathery external gills, a somewhat laterally flattened body and a long tail with dorsal and ventral fins. The forelimbs may be partially developed and the hind limbs are rudimentary in pond-living species but may be rather more developed in species that reproduce in moving water. Pond-type larvae often have a pair of balancers, rod-like structures on either side of the head that may prevent the gills from becoming clogged up with sediment. Some members of the genera "Ambystoma" and "Dicamptodon" have larvae that never fully develop into the adult form, but this varies with species and with populations. The northwestern salamander ("Ambystoma gracile") is one of these and, depending on environmental factors, either remains permanently in the larval state, a condition known as neoteny, or transforms into an adult. Both of these are able to breed. Neoteny occurs when the animal's growth rate is very low and is usually linked to adverse conditions such as low water temperatures that may change the response of the tissues to the hormone thyroxine. Other factors that may inhibit metamorphosis include lack of food, lack of trace elements and competition from conspecifics. The tiger salamander ("Ambystoma tigrinum") also sometimes behaves in this way and may grow particularly large in the process. The adult tiger salamander is terrestrial, but the larva is aquatic and able to breed while still in the larval state. When conditions are particularly inhospitable on land, larval breeding may allow continuation of a population that would otherwise die out. There are fifteen species of obligate neotenic salamanders, including species of "Necturus", "Proteus" and "Amphiuma", and many examples of facultative ones that adopt this strategy under appropriate environmental circumstances.